Lift trucks having hydraulically actuated telescopic masts are well known. For example, such trucks are manufactured and commercially marketed by the Raymond Corporation which is located in Greene New York and which has distributors throughout the United States and in several foreign countries.
A lift truck can be operated more rapidly and safely if the operator has as much unobstructed space in front of him as possible. The operator's visibility in a lift truck with telescopic mast sections is sometimes impeded by the presence of the hydraulic hoses which are necessary to supply pressurized oil to the cylinders on the fork carrier.
It is known that operator visibility can be improved by the use of a mast structure which has reeved hoses which are threaded over pulleys located on the top of the two movable mast sections. In such a mast structure the movable mast sections must be interconnected so that the inner telescopic section and the outer telescopic section move synchronously, thereby avoiding the application of undue tension on the reeved hoses. In a prior art system, the movement of the inner and outer telescopic sections is synchronized by means of a chain that is connected between the inner (i.e. upper) telescopic section and the fixed mast or truck main frame, with an idler sprocket connected to the outer (i.e. lower) telescopic section. As a result of this connection, the outer telescopic section is forced to move at one half the speed of the inner telescopic section. Stated differently, the relative speed of motion between the inner telescopic section and the outer telescopic section equals the relative speed between the outer telescopic section and the fixed mast. The hydraulic hoses have fixed connections to the bottom of the mast mainframe and to the bottom of the inner telescopic section, and they are reeved over idler pulleys which are journaled to the top of the outer telescopic section. Thus, the hoses remain taught.
A disadvantage associated with this prior art system is that the chain which interconnects the telescopic sections is positioned behind the mast, and in order to prevent the cross ties on the telescopic sections from interfering with the operation of the chain, the cross ties are positioned behind the chain. This structure undesirably increases the length of the overall lift truck.
The length of a lift truck is a very important characteristic of a lift truck, since turning radius is directly related to length. The productivity of a truck and operator is directly related to the turning radius of the truck. The elimination of one or more inches in the length of a truck therefore has significant economic significance.